During bending and lifting activities, erector spinae muscles must generate a large extensor moment to raise the upper body, and the object lifted, into an upright position (McGill and Norman, 1986). Since these muscles act on short lever arms, a high tensile force is required, and the lumbar intervertebral discs are subjected to a high compressive force. Occupations and tasks which demand frequent and heavy lifting are associated with a greatly increased risk of disc prolapses (Kelsey et al., 1984) and with low back pain in general (Kelsey and White, 1980). Indeed, severe chronic or acute low back injuries account for 25% of workers' compensation claims in the U.S. (Guo et al, 1995).
Injury prevention strategies include educating workers regarding proper techniques for lifting, sharing lifting tasks between several workers, and using mechanical aids for lifting (Waters and Putz-Andersson, 1994). Mechanical lifting devices, such as hoists, are effective in eliminating muscle strain when loads are beyond human lifting capability. However, when loads are within perceived human lifting capability, there is a tendency for subjects to lift manually as most mechanical lifting aids are slower than human speed and may not be easily accessible (Kazerooni, 2002).
Devices that are worn and support subjects in performing lifts have been proposed. An example of such a device is a lifting belt which acts as a rigid band around the waist, thus increasing intra-abdominal pressure. Current research findings suggest that lifting belts are not an effective means of reducing spinal loads (McGill, 1993 and 2002; NIOSH, 1994; Lavender et al., 2000; Chen, 2003), but might enhance spinal stability (Cholewicki, 2004; Hodges et al., 2004). However, it has been shown that wearing a lifting belt increases blood pressure which may increase the incidence of hemorrhoids, hernias, and varicose veins, particularly testicular varicose veins (Harman et al., 1989; Rafacz and McGill, 1996).
There is a need for an affordable effective device which is comfortably worn and helps a subject to perform activities that can otherwise lead to muscle strain.